Gas discharge lighting may involve a glass vessel containing low pressure gas and a plurality of electrodes used to ignite the gas. The electrodes supply electrons for the discharge and may be of the cold- or hot-cathode variety. In cold-cathode lamps the gas is ignited by ion bombardment, and in the hot-cathode variety the gas is lit by thermionic emission. In the case of general lighting, the gas discharge contains both portions of visible light and ultraviolet radiation—the spectral output of both depending mainly on the mixes of gases used, the pressure of the gas, the addition of mercury, amalgams, metals, alloys, elements, or combinations thereof. The addition of these components to the lamp also may affect the ease with which the lamps are operated and the steadiness and consistency of the output desired from the lamp.
Phosphors may be added to the inner walls of the lamp to further modify the output of the lamps by increasing the efficiency of visible light portions of the spectrums emitted. Typically, these phosphors are used to convert portions of the ultraviolet spectrums emitted by the mixtures into visible light to make them more efficient or pleasing for general lighting purposes. Black-lights, ultraviolet lamps, germicidal lamps, and spectrum lamps are all gas discharge lamps made of special glasses used to transmit or block portions of the UV and/or visible spectrum for optical or scientific purposes, air or water purification, the curing of glue and adhesives, reaction of chemical processes, germicidal use, the production of catalysts through advanced oxidation processes, and other kindred applications.
The lifespan of gas discharge bulbs may be limited by several factors. One limiting factor is a decreased efficiency of the lamps over time. Typically, this gradual inefficiency is due to a blackening of the inner walls of the glass tubes known in the art as “solarization.” In the construction of cold-cathode tubes it is caused by a gradual “sputtering” of the electrodes in starting and in operation where small portions of the metal electrodes are deposited on the glass walls as impurities over time, thus limiting the output. In the construction of hot-cathode lamps tungsten filaments contained on either end of the lamps become incandescent and portions of the metal filaments are boiled off during the thermionic emission process in the starting the lamps. The introduction of tungsten filaments also can also cause lamps to fail prematurely due to mechanical stresses or breakage as in the case of standard incandescent bulbs. In both styles of lamps, the operating voltage, frequency, and current must be critically matched for each lamp to avoid early lamp failures. In both styles of bulbs, there is also a chance of premature failure due to the leakage of the glass-to-metal seals used to secure the metal electrodes into the glass walls of the tube.
In the case of lamps constructed for general lighting, this blackening obscures the ultraviolet portion of the spectrum from reaching the phosphors and causes a reduced output of visual light and efficiency of the lamps over time. In the case of lamps used for the production of ultraviolet radiation, this blackening may also cause chemical reactions with the quartz and/or other glass used in the construction of these lamps, which may also cause a decrease in the ultraviolet production of the lamp. In both types of lamps, this gradual inefficiency may exist and increase even with no apparent detection in the normal starting and operation of the lamps. This may cause lamps to remain in service for periods of time where their usefulness has been reduced to the point of inefficiency.
A further disadvantage of conventional gas discharge lamps is the inability to properly dim the lamps in situations where reduced outputs are desired. Attempts to operate the lamps by varying the voltage or current often results in the lamps simply failing to light altogether, providing very little or no range as to how they are operated.